Windmills offer many advantages over other forms of power conversion devices. The cost of the power derived from the wind is usually proportional to the cost of maintenance of the windmill and accessories. In areas where the wind velocity is of a considerable magnitude during most of the year, the windmill provides independence, which in itself is a valuable and tangible reward and is easily worth the expenditure of the time required for the maintenance of the windmill apparatus.
Most windmills have a wheel, which includes a plurality of fixed pitch, radially spaced blades. The blades therefore must be set at an angle which represents a compromise between the wind blowing at a low velocity and at a high velocity. Various ingenius apparatus have been suggested in the past which can be employed to save the mill structure during winds of excessive velocity.
There are several disadvantages inherent in the design of a horizontal axis windmill of the type having radially arranged fixed blades. The wind gradient and the fixed pitch of the blades represent some of the most outstanding problems. The wind gradient in many parts of the country is a much greater problem than is realized by many mill mechanics. The wind forces simultaneously acting on the upper and lower marginal ends of the wheel often is many times greater on the upper end of the wheel as compared to the lower end thereof. The wind gradient therefore produces a large force differential on the blades, and this imbalance must be reckoned with in designing a large horizontal axis windmill.
A vertical axis windmill or turbine has many advantages over the horizontal axis windmill. In the vertical axis windmill, the wind gradient is less significant, the entire turbine assembly is more easily supported, and damage due to high velocity winds is more easily controlled. However, where the vertical axis rotor or wind turbine incorporates fixed pitch blades, there still must be a compromise by which the blade pitch is selected. Moreover, on many vertical axis turbines, the blades are effective for delivery of power only for a portion of the circumference of the rotating turbine wheel; and, in fact, a marginal circumferential length of the turbine may have blades which work in opposition to the other blades which are extracting power from the wind.
A vertical axis wind turbine which overcomes many of the above problems is the subject of this invention.